The field of the present invention relates generally to cable television and RF signal distribution equipment, and more specifically to multi-taps.
In cable TV and other RF distribution systems it is typically necessary to tap off a television or RF signal from a main distribution cable for bringing the television or RF signal into a customer facility on a secondary cable. The signal tapped off is generally substantially attenuated through use of a signal tapping device. A known device for accomplishing this is a multi-tap, that permits connection to the main television or RF signal carrying cable, and provides multiple outputs for individual connection to a number of customers, respectively. In a typical cable television distribution system, a plurality of multi-tap devices are connected as required along the length of a main signal line for tapping and distributing television signals to a plurality of the customers located in a vicinity of the areas where the main cable is strung. In such an installation, it is common practice to pass the main cable into one multi-tap at an input port thereof, and to continue the main cable from an output port of the multi-tap for connection to the input port of the next multi-tap down line. As more customers are added to the system, it may be necessary to lengthen the line, and/or to increase the level of power of the main television signal being conducted by the main cable. It is also typical to have the main distribution cable conduct both the television or RF signal along with the AC power necessary to energize the electronic circuitry of each of the multi-taps. It is often necessary to open one or more of the multi-taps connected in cascade, in order to change a tap plate for changing the attenuation or signal levels of the signals tapped off for connection to customers, in order to maintain the customers' signal level at an appropriate level of power (an appropriate dB level).
With known multi-taps of the prior art, whenever tap plates must be removed for substituting a new tap plate to obtain higher or lower attenuation, or to repair a particular multi-tap, the main RF signal and associated AC power for the multi-taps down line of the multi-tap being serviced are interrupted or cut off from the down line multi-taps. Accordingly, all customers inclusive of the customers associated with the multi-tap being serviced, and those down line, have their television signal connections interrupted until the servicing of the multi-tap under repair or conversion is completed. Many attempts have been made to overcome this difficulty.
In order to prevent this interruption in the flow of RF and AC to downstream users in the prior art, a jumper tool typically provided by a shunt coaxial cable is coupled between an unused input port and an unused output port of the multi-tap. Whereas this works well when the tap plate just described is removed, the shunt coaxial cable ceases to function as a transmission line when the tap plate is installed and acts instead like an impedance in shunt with the circuit because of a double termination. This double termination prevents a 75 ohm impedance match at the associated junctions. This impedance mismatch causes standing waves with numerous transmission nulls such that a true 75 ohm transmission line does not exist. The effect is to cause significant variation in the frequency response within the band of channels flowing along the transmission line, both for the multi-tap to which it is connected and to downstream users.